Pneumatic safety circuit for air inflation devices

ABSTRACT

The invention provides an improved pneumatically operated circuit for automatically shutting off the flow of high pressure air being introduced into an object to be inflated, such as a tire, when the pressure in the object reaches a preselected maximum pressure significantly below that of the high pressure supply. The air at high pressure is introduced into the object and into a control duct also connected to the object, until pressure in the control duct overcomes the bias of a control valve, at which time the control valve closes to interrupt the flow of high pressure air and allow pressure in the object and the control duct to equilibrate; if the equilibrated pressure does not continue to overcome the bias of a control valve, the control valve again opens to admit additional high pressure air to the object and control duct until the bias of the control valve again is overcome and the control valve closed as previously, repeating the closing cycle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to pneumatic safety circuits for air inflationdevices. More particularly, it relates to pneumatic safety circuits thatcan be installed in the pneumatic circuits of tire inflating machines ortire mounting machines being built by a machine manufacturer and alsocan be installed on existing tire inflating machines or tire mountingmachines which are generally devoid of pneumatically operated safetycircuits, to retrofit them and upgrade their safety standards.

2. Description of the Prior Art

In garages and tire installation and repair shops, a supply of highpressure, "shop" air is available to operate the pneumatic portion oftire mounting machines that are used to press, lever, and wedge tiresoff or onto tire rims or automobile wheels. The same air supply, at theshop pressure usually in the range of 125 and 175 psi, (862 to 1207KPa), is used to inflate the tires to the appropriate tire pressureusually in the range of 30-50 psi, (207 to 345 KPa), to insure they arein place on the wheels. In order to seat the beads of a modern tire tothe rim, it is sometimes necessary to overinflate the tire temporarily,after which the tire pressure is reduced to the desired runningpressure. Also, the tires often are inflated before a valve core isinstalled in the valve stem, to expedite build-up of pressure in thetire. With no valve core in the valve stem, tire pressure can build upextremely rapidly with shop air.

Control of pressure build-up in the tire generally is achieved byoperation of a pneumatic supply valve, either manual or pedal operated,which opens and closes in the line from the shop air supply to the tirebeing inflated. A pressure gauge in this line indicates, when the supplyvalve is closed and the line connected to the tire, what the pressure inthe tire is. By intermittently operating the supply valve, the build-upof pressure in the tire can be monitored, but careless or inattentiveoperation of the supply valve has been known to overinflate and bursttires, causing serious damage to personnel and property.

To preclude such accidents, it has been suggested to have additionalswitching facilities to control the shop air supply, but thesefacilities appear primarily to involve electrical circuitry, making theminappropriate or useless for retrofitting existing tire mountingmachines which are entirely pneumatic in operation. Furthermore, theadditional switching facilities generally operated by merely reducingthe pressure being applied to inflate a tire, thus greatly retarding therate of inflation and inducing operators to bypass them to expeditetheir work.

In a Canadian patent application Serial No. 590114 filed 3 Feb. 1989 byMichael C. Molls and corresponding U.S. application Ser. No. 316,283filed 27 Feb. 1989, there is disclosed a pneumatically operated safetycircuit which automatically shuts off the flow of high pressure airbeing introduced into a tire when the pressure in the tire reaches apreselected maximum pressure significantly below the high pressure airsupply. The high pressure air is supplied to the tire through athree-way pilot operated pneumatic valve whose position is alternatedbetween an inflating cycle and a gauging cycle by operation of a pair oftime-delay three-way pilot operated pneumatic valves which are set toallow high pressure air to inflate the tire for a first timed period,then interrupt high pressure air to the tire and for a second timedperiod, generally much briefer than the first timed period, gauge thepressure in the tire and, if the tire pressure has achieved the desiredmaximum pressure, interrupt the inflating cycle by maintaining thethree-way pilot operated pneumatic valve in the gauging position. Thesafety circuit required the use of two time-delay three-way valves andinvolves greater expense for construction than can be achieved with thepneumatic circuit of the present invention.

SUMMARY OF THE INVENTION

The present invention consists of a pneumatic circuit for air inflationdevices having a high pressure pneumatic supply line connected to anobject to be inflated to a pressure significantly lower than the supplyline pressure, through an operator controlled valve in said highpneumatic supply line, said pneumatic circuit comprising:

1) a first pneumatic duct connecting high pressure air from the outletof said operator controlled valve to the inlet of a three-way pilotoperated valve normally biased to a first position in which air pressureat the said inlet is transmitted through the valve then by a secondpneumatic duct directly to the pilot side of

2) a spring biased, normally closed, pilot opened, two-way valve, saidthree-way pilot operated valve being adapted to overcome its bias bypneumatic pressure in its pilot which moves said there-way pilotoperated valve to a second position in which air pressure in said secondpneumatic duct is discharged back through said three-way valve toatmosphere;

3) a third pneumatic duct connecting high pressure air from the outletof said operator controlled valve to the inlet of said spring biasedtwo-way valve;

4) a fourth pneumatic duct connecting the outlet of said spring biasedtwo-way valve to an object to be inflated, and;

5) a pneumatic control duct connecting said fourth pneumatic ductthrough a pneumatic flow control to a first pilot on said three-waypilot operated valve, the bias of said three-way pilot operated valvebeing adapted to maintain said three-way pilot operated valve in saidfirst position when the pressure in said pneumatic control duct is belowthe pressure to which the object is to be inflated.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood from the followingdescription thereof taken in conjunction with the accompanying drawingsin which:

FIG. 1 is a schematic drawing, using available ANSI symbols, of apneumatic circuit of the invention incorporated in a simple pneumatictire inflating device, with some optional features included forincreased convenience and assured safety;

FIG. 2, another embodiment of the invention, is a schematic drawing of apneumatic circuit similar to FIG. 1 and having some different optionalarrangements;

FIG. 3, another embodiment of the invention, is a schematic drawing ofanother pneumatic circuit having different optional alternativearrangements and being suitable for inflation of truck tires.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, the term duct is intended to include any tube, pipe,enclosed channel, enclosed canal, or open-ended line capable ofmaintaining or conducting air under pressure without loss between itsopen ends. In the accompanying schematic drawings of the pneumaticcircuits, the symbols used for the various pneumatic components arethose adopted by the American National Standards Institute (ANSI) forsuch components; in the various Figures of the drawings, the samelegends are used throughout it to identify identical parts.

In FIG. 1, legend 10 indicates a high pressure air supply line leadingfrom an operator's pedal controlled or manually controlled valve, shownby a conventional sign f or a pneumatic supply. The supply convenientlycomes from a commercial air compressor at a pressure in the range from125 psi to 175 psi (862 KPa to 1207 KPa) and most conveniently is in therange of 140 to 150 psi (955 Kpa to 1034 KPa). The operator controlledvalve conveniently is spring biased in the closed position and ismaintained open only by the sustained action of an operator, althoughwith pneumatic circuit of the present invention it need not be springbiased. However, it is preferred that it be so biased, as an extrasafety feature against operator inattention.

Preferably air from the supply line 10 passes first through an optionalair filter, 11, to remove entrained solids and liquids that couldinterfere with the operation of pneumatic components. Air from thesupply then passes via a first duct to an inlet of a three-way, pilotoperated, biased, normally open valve, 13, through which in this firstposition air passes, then via a second duct 14 to pressurize the pilotof a two-way pilot operated, spring biased, normally closed valve 15. Assoon as the pilot of valve 15 is pressurized, valve 15 opens to pass airat high pressure from duct 12 through third duct 16, valve 15, andfourth duct 17, to the inlet of a tire or other object to be inflated,18.

Because the volume of a tire or other object to be inflated is generallyvery large compared to the volume of the ducts or lines associated withinflating it, pressure in the tire builds up more slowly than in theassociated lines or ducts, particularly if there is a valve core in thevalve stem of the tire. Thus in control duct 38 extending from duct 17beyond the connection to tire 18 from the supply line, pressure buildsup in control duct 38 to ducts leading to fixed choke or other flowcontrol 19 and optional features 21, 22, 23 and 24 to be describedlater.

The fixed choke or flow control 19 reduces the rate at which pressurebuilds up on the pilot of valves 13 and prolongs the period ofapplication of pressure through line 17 to tire 18 before the pilotcloses valve 13 by overcoming its bias. As soon as valve 13 does move toits second position, i.e., close, pressure in duct 14 discharges backthrough valve 13 to the atmosphere, thus allowing valve 15 to close byits spring bias and thus interrupting flow of high pressure air to duct17 and tire 18. Immediately after valve 15 closes, air pressure on thepilot of valve 13 flows back through choke or flow control 19 andcontrol duct 38, and equilibrates with the pressure in the much largervolume of tire 18. If that pressure then has not reached the value towhich the tire is to be inflated and is not sufficient to overcome thebias of valve 13, then valve 13 is reopened by its bias, air supplypressure is applied to the pilot of valve 15, which opens, and highpressure air again is admitted through valve 15 to duct 17 and tire 18until pressure again builds up on the pilot of valve 13 until itovercomes the bias of valve 13 and again closes it. The cycling of valve13 closing and opening is repeated until the tire pressure achieves thevalue at which the bias of valve 13 is selected to allow valve 13 toremain closed.

A number of optional features can be added to the circuit to, amongother things, increase the safety characteristics of the circuit andincrease its flexibility. These features shown in FIG. 1 include a firstpressure relief means, for example a pop safety valve, a spring checkvalve, or a side outlet relief valve 21, as illustrated in FIG. 1; thismeans is connected to duct 38 and can be set to discharge to atmosphereat a preselected pressure in duct 38 somewhat above the final pressureto which the tire 28 is to be inflated, thereby helping to ensure thatpressure in duct 38 and tire 28 does not exceed the preselected level. Asecond optional feature illustrated in FIG. 1 is a pressure gauge 22connected to duct 38 which, when valves 15 and 13 both are closed andduct 38 contains only the pressure in tire 18, registers that tirepressure. A third optional feature illustrated in FIG. 1 is a secondpressure relief means also connected to duct 38 to serve as a back-up toside outlet relief valve 21, and is shown as a second side outlet valve23. A fourth optional feature is a pressure bleed valve, 24, which is aspring biased, normally closed, manually opened, two-way valve by whichthe pressure in duct 38 and tire can be manually discharged to theatmosphere. A final optional feature shown in FIG. 1 is an over-ridearrangement by which the tire can be inflated beyond the pressure towhich the bias of valve 13 is selected to limit it. The over-ridearrangement includes a spring biased, normally closed, manually opened,two-way valve, 25, connected to duct 16; on being manually opened, valve25 admits high pressure air supply, through fifth duct 26 to the inletof a pressure regulator, 27, which can be of adjustable type asillustrated or fixed. The outlet of the pressure regulator is connectedby sixth duct 28 to duct 17 and, when valve 25 is open, permits air, ata regulated pressure much lower than the high pressure air supply, tocontinue inflating the tire at a rate which consequently is much slowerthan occurs when valve 15 is open. As a result the tire can be furtherinflated slowly while the pressure therein is monitored, for examplevisually by pressure gauge 22 to achieve a value exceeding the pressurelimit set f or the tire by the bias of valve 13. The maximum pressure towhich the tire could be inflated by this arrangement is the pressurepermitted by the pressure regulator, which pressure can be adjusted ifthe regulator is of the adjustable type or preselected for anappropriate value if a fixed type regulator is used. In any event, theover-ride feature permits the gradual addition of pressure to tire up toan appropriate maximum which is greater than the maximum to which thetire can be safely be rapidly inflated by high pressure air throughvalve 15 in its open position. Such open position is not maintained whenthe pressure in tire 18 is sufficient to close valve 13 by overcomingits bias, and thus bleed line 14 and the pilot of valve 15, allowing thespring bias of valve 15 to close same.

It will be noted that the bias of valve 13 has not been defined simplyas a spring bias, although it is shown as such in FIG. 1. This isbecause in practice the bias could be maintained, either in part orcompletely, by means other than a spring. The embodiments of theinvention in FIGS. 2 and 3 illustrate these two options respectively.

The embodiment of the invention illustrated in FIG. 2 operates basicallyin the same manner as that in FIG. 1, up to the point where the tire hasbeen inflated to the pressure at which the pressure in control duct 38remains above that required to overcome the spring bias keeping valve 13in its first position; at this point valve 13, remains in its secondposition, line 14 is bled to atmosphere and valve 15 remains closedunder its spring bias. If it is now desired to over-ride the circuit andadmit additional air pressure to the tire, a spring biased, normallyclosed, manually operated, two-way valve, 29, connected to duct 38 , ismanually opened by the operator to admit air at the pressure in duct 38and in the tire 18 to the inlet of a pressure regulator, 30, which canbe of the adjustable type as illustrated in FIG. 2 or a fixed type (notshown). In either case air at reduced pressure from the outlet of theregulator is led by seventh duct, 31, to a second pilot on valve 13.This air pressure on the second pilot adds pilot pressure bias to theopen position of the valve, and supplements the bias of the spring whichtends to keep valve 13, open, thus overcoming the pressure in duct 38which has closed valve 13 and permitting it to admit high pressure airto duct 14 again, thus opening valve 15 by its pilot and again admittinghigh pressure air to line 17 and tire 18. The pressure regulator 30precludes the pressure on the second pilot from adding more than apreselected amount of bias to the bias provided by the spring of valve13 (or a fixed amount of bias pressure regulator of the fixed type isused). Thus if valve 29 is manually held open to over-ride the initialbias of valve 13 which limits the pressure built up in tire 18, valve 13still operates to limit the pressure built up in tire 18, albeit thebuilt-up pressure is greater when valve 29 is open, the increment beingset by the setting or characteristics of pressure regulator 30 throughwhich supplemental pressure bias is added to the spring bias of valve13. A less preferred form of the embodiment of FIG. 2 has a simple choke30A in duct 31 instead of a pressure regulator 30. Such an arrangementpermits the over-ride to add an unlimited amount of supplemental pilotpressure bias to the spring bias of valve 13, thus permitting a greaterbuild-up of pressure in the tire, which build-up would have to bemonitored visually on the pressure gauge and interrupted by closure ofvalve 29 when the desired amount of build-up has been achieved. To guardagainst operator inattention or faulty operation of the pressure gauge22 if a choke 30A is used instead of a pressure regulating valve 30 induct 31, it is imperative, for safety reasons, to have a third pressurerelief means, for example a side outlet relief valve, 30B, connected toduct 31 and set to discharge to atmosphere when the pressure in line 31goes significantly (i.e., to an unsafe level) above that required toprovide the necessary pilot pressure and supplementary bias to openvalve 13. Pressure relief means 21 and 23 also prevent unlimitedbuild-up from exceeding the safe pressure limit at which these means aredesigned to discharge control duct 38 to atmosphere, whether they areside outlet relief valves, as shown, or simple pop valves or springcheck valves, as mentioned with reference to FIG. 1.

The embodiment of the invention illustrated FIG. 3 differs again fromthat of FIG. 1 in the way valve 13 is operated, and also from that ofFIG. 2 in the same respect. The pneumatic circuit of FIG. 1 uses only aspring bias to hold valve 13 in its normally open position. The circuitof FIG. 2 uses spring bias to hold valve 13 in its open position untilthe optional over-ride feature is manually put into operation, at whichtime the spring bias is supplemented by pressure in line 31 to a secondpilot on valve 13, assisting the spring in maintaining valve 13 open.The circuit of FIG. 3 does not have any spring bias to hold valve 13 inits normally open position. The necessary bias to maintain valve 13 inits normally open position is provided by air pressure from first duct13, taken through an eighth duct, 32, through an adjustable or fixedpressure regulator, 33, and ninth duct, 34, to the second pilot on valve13. The regulated air pressure provided by pressure regulator 33 in duct34 to second pilot of valve 13 provides a uniform bias comparable to theuniform bias provided by the spring in valve 13 of FIG. 1. Thus when airfrom the supply line 10 is admitted to the pneumatic circuit, valves 13and 15 operate exactly as they do in the embodiment described in FIG. 1,until the pressure in tire 18 reaches the value to which it is to beinflated and the steady pressure therein, through duct 38 and the firstpilot on valve 13, closes valve 13 by overcoming the bias provided bythe second pilot and pressure in duct 34. The appropriate pressure induct 34 to provide the desired bias for the second pilot of valve 13 isobtained by selection of an appropriate fixed pressure regulator 33, oradjustment of an alternative corresponding adjustable pressure regulatorto provide only sufficient pressure in duct 34 to maintain valve 13 openuntil air pressure in tire 18, exerted through control duct 38, hasreached the preselected value and closes valve 13 through the firstpilot thereon. Should it then be desired to raise the pressure in tire18 somewhat above the preselected value under manual control, anoptional over-ride arrangement is provided by tenth duct 35 connected tothe high pressure supply, for example duct 16, and containing a choke 36and spring biased, normally closed, manually opened, two-way valve 37,discharging into duct 38. The additional pressure thus provided in duct38 not only ensures that valves 13 and 15 are kept in their closedpositions, but also further inflates tire 18 by air flow in duct 38 indirection reverse to the normal air flow in duct 38 during inflation ofthe tire. Pressure relief valves 21 and 23, set to discharge pressure induct 38 to atmosphere if it goes above a safe level, ensure that theover-ride arrangement is not abused to over-inflate the tire to anunsafe extent, and gauge 22 enables the operator operating the manualover-ride to monitor the pressure in tire 18 as it builds up above thepreselected value.

Numerous other modifictions may be made to the specific embodiments andexpedients described without departing from the present invention, thescope of which is defined in the following claims.

What is claimed is:
 1. A pneumatic circuit for air inflation deviceshaving a high pressure pneumatic supply line connected to an object tobe inflated to a pressure significantly lower than the supply linepressure, through an operator controlled valve in said high pressurepneumatic supply line, said pneumatic circuit being operative forstopping inflation once a preselected pressure is equalled, saidpneumatic circuit comprising:1) a first pneumatic duct adapted forconnecting high pressure air from the outlet of said operator controlledvalve to the inlet of a two-position three-way pilot operated valvehaving non-adjustable biasing means for being normally biased to a firstposition in which air pressure to the said inlet is transmitted throughthe valve then, by a second pneumatic duct, directly to the pilot sideof 2) a spring biased, normally closed, pilot opened, two-way valve,said three-way pilot operated valve being adapted to overcome its biasby pneumatic pressure in its first pilot which moves said three-waypilot operated valve to a second position in which air pressure in saidsecond pneumatic duct is discharged back through said three-way valve toatmosphere, 3) a third pneumatic duct connecting high pressure air fromthe outlet of said operator controlled valve to the inlet of said springbiased two-way valve, 4) a fourth pneumatic duct adapted for connectingthe outlet of said spring biased two-way valve to an object to beinflated, and 5) a pneumatic control duct connecting said fourthpneumatic duct through a pneumatic flow control to said first pilot onsaid two-position three-way pilot operated valve, the bias of saidtwo-position three-way pilot operated valve being adapted to maintainsaid two-position three-way pilot operated valve in said first positionwhen the pressure in said pneumatic control duct is below the pressureto which the object is to be inflated.
 2. A pneumatic circuit as claimedin claim 1 in which the bias to maintain the said three-way pilotoperated valve in said first position is a spring bias.
 3. A pneumaticcircuit as claimed in claim 2 and further including a spring biased,normally closed, manually opened, two-way valve with its inlet connectedto said pneumatic control duct and its outlet connected through apressure regulator to a second pilot on said three-way, pilot operatedvalve normally biased to said first position, said second pilotsupplementing the bias of said three-way pilot operated valve tomaintain it in said first position.
 4. A pneumatic circuit as claimed inclaim 3 and further including:(a) at least one pressure relief meansconnected to said pneumatic control duct and adapted to discharge toatmosphere the pressure in said pneumatic control duct at a preselectedpressure in said duct above the final pressure to which the object is tobe inflated, (b) a pressure gauge connected to said pneumatic controlduct, and (c) a manually operable pressure bleed valve connected to saidpneumatic control duct.
 5. A pneumatic circuit as claimed in claim 2 andfurther including(a) a spring biased, normally closed, manually opened,two-way valve with its inlet connected to said pneumatic control ductand its outlet connected through a choke to a second pilot on &aidthee-way, pilot operated valve normally biased to said first position,said second pilot supplementing the bias of said three-way pilotoperated valve to maintain it in said first position, and (b) a pressurerelief means connected to said second pilot and adapted to discharge toatmosphere when the pressure on the second pilot goes to a preselectedlevel above the required to provide supplementary bias to saidthree-way, pilot operated valve.
 6. A pneumatic circuit as claimed inclaim 5 and further including at least one pressure relief meansconnected to said pneumatic control duct and adapted to discharge toatmosphere the pressure in said pneumatic control duct at a preselectedpressure in said duct above the final pressure to which the object is tobe inflated,(b) a pressure gauge connected to said pneumatic controlduct, and (c) a manually operable pressure bleed valve connected to saidpneumatic control duct.
 7. A pneumatic circuit as claimed in claim 1 inwhich the bias to maintain the said three-way pilot operated valve insaid first position is a second pilot on said pilot operated valve, saidsecond pilot being operated by reduced pneumatic pressure from apressure regulator connected to said first pneumatic duct.
 8. Apneumatic circuit as claimed in claim 7 in which the pressure regulatoris a fixed pressure regulator.
 9. A pneumatic circuit as claimed inclaim 8 and further including a spring biased, normally closed, manuallyopened, two-way valve with its inlet connected through a choke to thehigh pressure air supply in said first duct and its outlet connected tosaid control duct.
 10. A pneumatic circuit as claimed in claim 9 andfurther including at least one pressure relief means connected to saidpneumatic control duct and adapted to discharge to atmosphere thepressure in said pneumatic control duct at a preselected pressure insaid duct above the final pressure to which the object is to beinflated,(b) a pressure gauge connected to said pneumatic control duct,and (c) a manually operable pressure bleed valve connected to saidpneumatic control duct.
 11. A pneumatic circuit for air inflationdevices having a high pressure pneumatic supply line connected to anobject to be inflated to a pressure significantly lower than the supplyline pressure, through an operator controlled valve in said highpressure pneumatic supply line, said pneumatic circuit comprising:1) afirst pneumatic duct adapted for connecting high pressure air from theoutlet of said operator controlled valve to the inlet of a three-waypilot operated valve normally biased to a first position in which airpressure to the said inlet is transmitted through the valve then, by asecond pneumatic duct, directly to the pilot side of 2) a spring biased,normally closed, pilot opened, two-way valve, said three-way pilotoperated valve being adapted to overcome its bias by pneumatic pressurein its first pilot which moves said three-way pilot operated valve to asecond position in which air pressure in said second pneumatic duct isdischarged back through said three-way valve to atmosphere, 3) a thirdpneumatic duct connecting high pressure air from the outlet of saidoperator controlled valve to the inlet of said spring biased two-wayvalve, 4) a fourth pneumatic duct adapted for connecting the outlet ofsaid spring biased two-way valve to an object to be inflated, 5) apneumatic control duct connecting said fourth pneumatic duct through apneumatic flow control to said first pilot on said three-way pilotoperated valve, the bias of said three-way pilot operated valve beingadapted to maintain said three-way pilot operated valve in said firstposition when the pressure in said pneumatic control duct is below thepressure to which the object is to be inflated, and 6) at least onepressure relief means connected to said pneumatic control duct andadapted to discharge to atmosphere the pressure in said pneumaticcontrol duct at a preselected pressure in said duct above the finalpressure to which the object is to be inflated.
 12. A pneumatic circuitas claimed in claim 11 and further including a pressure gauge connectedto said pneumatic control duct.
 13. A pneumatic circuit as claimed inclaim 12 and further including a manually operable pressure bleed valveconnected to said pneumatic control duct.
 14. A pneumatic circuit asclaimed in claim 13 and further including (1) a spring biased normallyclosed, manually opened two-way valve with its inlet connected to saidthird duct and its outlet connected to the inlet of (2) a pressureregulator having its outlet connected to said fourth duct, said pressureregulator being adapted to increase the pressure in said fourth duct.15. A pneumatic circuit as claimed in claim 14 in which the bias tomaintain the said three-way pilot operated valve in said first positionin a spring bias.